bridge: add root port blocking

This is Linux bridge implementation of root port guard.
If BPDU is received from a leaf (edge) port, it should not
be elected as root port.

Why would you want to do this?
If using STP on a bridge and the downstream bridges are not fully
trusted; this prevents a hostile guest for rerouting traffic.

Why not just use netfilter?
Netfilter does not track of follow spanning tree decisions.
It would be difficult and error prone to try and mirror STP
resolution in netfilter module.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index c331e28c7880..65429b99a2a3 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -27,6 +27,7 @@ static inline size_t br_port_info_size(void)
                 + nla_total_size(4)     /* IFLA_BRPORT_COST */
                 + nla_total_size(1)     /* IFLA_BRPORT_MODE */
                 + nla_total_size(1)     /* IFLA_BRPORT_GUARD */
+                + nla_total_size(1)     /* IFLA_BRPORT_PROTECT */
                 + 0;
 }
 
@@ -51,7 +52,8 @@ static int br_port_fill_attrs(struct sk_buff *skb,
             nla_put_u16(skb, IFLA_BRPORT_PRIORITY, p->priority) ||
             nla_put_u32(skb, IFLA_BRPORT_COST, p->path_cost) ||
             nla_put_u8(skb, IFLA_BRPORT_MODE, mode) ||
-            nla_put_u8(skb, IFLA_BRPORT_GUARD, !!(p->flags & BR_BPDU_GUARD)))
+            nla_put_u8(skb, IFLA_BRPORT_GUARD, !!(p->flags & BR_BPDU_GUARD)) ||
+            nla_put_u8(skb, IFLA_BRPORT_PROTECT, !!(p->flags & BR_ROOT_BLOCK)))
                 return -EMSGSIZE;
 
         return 0;
@@ -165,6 +167,7 @@ static const struct nla_policy ifla_brport_policy[IFLA_BRPORT_MAX + 1] = {
         [IFLA_BRPORT_PRIORITY]  = { .type = NLA_U16 },
         [IFLA_BRPORT_MODE]      = { .type = NLA_U8 },
         [IFLA_BRPORT_GUARD]     = { .type = NLA_U8 },
+        [IFLA_BRPORT_PROTECT]   = { .type = NLA_U8 },
 };
 
 /* Change the state of the port and notify spanning tree */